Hoping to head off another confirmation battle, the White House said Tuesday that it will allow senators to review a secret paper justifying the drone strike on an American citizen written by one of President Obama's appellate court nominees.

Some legal scholars and human rights activists argue it was illegal for the U.S. to kill American citizens away from the battlefield without a trial.

The American Civil Liberties Union wrote a letter to senators on Monday, urging them to delay Barron's confirmation vote until all senators review memos he wrote on the drone program. Republican Sen. Rand Paul of Kentucky also is trying to block Barron's confirmation, barring public release of a redacted version of the al-Awlaki memo, by virtue of a court order.

Paul last year held up the nomination of CIA Director John Brennan until the administration agreed to release more information about its drone policy. And other Obama nominees, including the president's picks for surgeon general and chief civil rights attorney, have failed to win confirmation this year in the Democratic-controlled Senate amid controversy raised by interest groups.

In Barron's case, the White House quickly responded to the ACLU by offering to show senators an unredacted copy of the 41-page memo he authored July 16, 2010, which argues that targeted killing of an American citizen overseas does not violate the Constitution.

White House spokesman Eric Schultz noted that members of the Senate Judiciary Committee, which advanced Barron's nomination on a party-line vote, already had access to the memo. Schultz expressed confidence that Barron would be confirmed and "bring outstanding credentials, legal expertise and dedication to the rule of law to the federal bench."

The Second U.S. Circuit Court of Appeals in New York ruled last month that the Obama administration must publicly disclose a redacted version of the memo. The administration is considering whether to appeal the ruling.

Chris Anders, the ACLU's senior legislative counsel, said that Barron reportedly signed at least two memos on the drone program and that all his opinions should be revealed to senators, not just the one. "This is short-changing senators who should be getting information that they need to review before voting on a lifetime appointment," Anders said.

At least one Democrat, Sen. Mark Udall of Colorado, said he won't support Barron unless the White House complies with the court order to publicly disclose a redacted version of Barron's memo. Another Democrat, Sen. Ron Wyden of Oregon, also called for the drone memos to be released publicly but isn't yet taking a position on Barron's confirmation.